An implantable medical device, for the delivery of stimulation therapy, may include an electrode and a fixation component configured to hold the electrode in intimate contact with tissue at a stimulation site. One type of such a device may be a traditional implantable cardiac pacemaker that includes a pulse generator and a pacing electrode coupled to the generator by an elongate insulated lead wire. The pulse generator is typically implanted in a subcutaneous pocket, remote from the heart, with the lead wire extending therefrom to a pacing site where the electrode is positioned. Another type of implantable medical device may be one wholly contained within a relatively compact package for implant in close proximity to the pacing site. FIG. 1 illustrates such a device 100 including an hermetically sealed housing 105, preferably formed from a biocompatible and biostable metal such as titanium, that contains an electronic controller and associated power source (not shown), to which at least one electrode 111 is coupled, for example, by a hermetic feedthrough assembly (not shown).
With further reference to FIG. 1, device 100 has been deployed by an operator via a delivery tool 200, which the operator has maneuvered up through the inferior vena cava IVC and across the right atrium RA into the right ventricle RV. The deployed device 100 is shown fixed at the pacing site by a fixation member 115 thereof, for example, including tissue-penetrating tines that surround electrode 111 and secure electrode 111 in intimate contact with tissue at the site. Further description of a suitable construction for device fixation member 115 may be found in the co-pending and commonly assigned United States Patent Application having the pre-grant publication number 2012/0172690 A1.
An alternative pacing site may be located on an epicardial surface of the heart, for example, on the left side of the heart for the application of pacing therapy to treat heart failure. FIG. 2 is a schematic showing an access site A for creating a passageway between a patient's diaphragm 19 and xiphoid process 20 of sternum 13, for example, to implant a pacing electrode on an epicardial surface 6 of the patient's heart, which is enclosed within the pericardial sac 15. After making a superficial incision, an operator may open a passageway between diaphragmatic attachments 18 and diaphragm 19 by using blunt dissection tools and techniques that are known in the art. Then, the operator may employ a piercing tool to pass a guide wire through the pericardial sac 15, also according to methods known in the art. The operator may use fluoroscopic guidance to position a distal portion of the guide wire along a portion of epicardial surface 6, at which a target site is located, and then pass a guiding sheath over the positioned guide wire. The guiding sheath then serves as a conduit for delivery of the implantable electrode to the target site. In this context, to deliver and then fix, or secure the implantable electrode at an epicardial site, there is a need for new configurations of interventional systems and associated implantable device assemblies.